Figure 38-1 Ventricular fibrillation. Note the absence of any type of visible recurrent pattern. This is a completely chaotic electrocardiographic representation of the chaotically contracting ventricles.
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Ventricular fibrillation (VFib) is defined as a rapid, completely disorganized ventricular rhythm. The electrocardiographic characteristics of this arrhythmia are undulations of varying shapes and sizes with no pattern and no discernible P, QRS, or T waves (Figure 38-1). The undulations occur anywhere from 150 to 500 times in a minute. Notice that we did not use the word “beats” to describe the undulations. This is because in VFib there is no organized beating of the heart in any way, shape, or form.
Figure 38-1 Ventricular fibrillation. Note the absence of any type of visible recurrent pattern. This is a completely chaotic electrocardiographic representation of the chaotically contracting ventricles.
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Some authors have commented on the presence of fine and coarse VFib (Figure 38-2). We saw the similar fine and coarse patterns for atrial fibrillation back in Chapter 20, Atrial Fibrillation The actual meaning or significance of the two electrocardiographic interpretations is unclear, but we will present the two variations. Keep in mind that sometimes, fine VFib is actually mistaken for asystole (or the absence of rhythm). In order to differentiate between the two, switching leads is extremely helpful. If you see the typical fibrillatory pattern in a different lead, then defibrillation is still indicated.
Figure 38-2 Coarse and fine ventricular fibrillation.
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DescriptionVFib is typically caused by increased automaticity of multiple ectopic ventricular pacemakers (Figure 38-3). In addition, many separate reentry circuits are created and are functioning at the same time in the ventricles. The net result is that there is no depolarization wave of any real value formed throughout the entire ventricle. Each small section contracts, but the chaos of the regional depolarizations and contractions essentially shuts down the ventricles. When there is no mechanical contraction, there is no cardiac output. This is a condition that is not compatible with life.
Figure 38-3 In the ventricular tissue there could be many, many individual ectopic foci acting as ectopic pacemakers at the same time. Most of these small islands of depolarization throughout the ventricles cancel each other out. These ectopic pacemakers, however, do create small vectors, which show up on the ECG strip as undulations of varying size and morphology. In addition, there are multiple reentry circuits formed and functioning at the same time. The net result is complete chaotic depolarization of the ventricles. This chaotic depolarization essentially shuts down mechanical contraction.
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Clinically, VFib can occur spontaneously in a patient with a normal heart. It is also common for ventricular tachycardia to deteriorate into VFib. However, the most common cause of the arrhythmia is an acute myocardial infarction. For many unfortunate patients, this lethal arrhythmia is the very first sign of an early acute myocardial infarction. Together with ventricular tachycardia, these two arrhythmias account for over 50% of the mortality associated with coronary artery disease.
VFib is a deadly arrhythmia. Spontaneous termination of the arrhythmia does not occur. If you get the arrhythmia, you die. The only chance of survival is immediate treatment. Within only 10 to 20 seconds of a cessation of cardiac output, life-threatening complications can begin. What is the most effective treatment for VFib? Immediate defibrillation. As we always say, electricity is our friend!
What exactly happens during defibrillation? The electrical stimulus provided by emergent defibrillation causes an immediate and synchronized depolarization of all ventricular myocytes (Figure 38-4). The heart is essentially externally stimulated, depolarized, and then left to fend for itself. Luckily, myocytes only remember as far back as the last electrical depolarization. The hope is that by shutting down the ectopic pacemakers and the reentry circuits, all during the same millisecond, the normal cardiac pacemakers will begin to take over synchronized and normal conduction of the electrical impulse throughout the heart. In essence, we stop the heart momentarily, in hopes that it will return to normal function.
Figure 38-4 Chaotic depolarization of the ventricles leads to ventricular fibrillation. Defibrillation leads to a state where all of the myocytes of the heart are depolarized instantaneously. This essentially resets all of the myocytes. The hope is that the normal cardiac pacemakers will then be able to take over pacing function and that transmission of the depolarization wave can proceed normally through the “reset” electrical conduction system and myocardium.
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DescriptionAdditional Information
Is It VFib or Artifact?
A clinical word of warning: Always treat the patient, not the arrhythmia! Many times, movement of the lead, the patient, or the patient’s intrinsic tremors can lead to misdiagnosis of a rhythm abnormality (Figures 38-5 through 38-8). Artifact can resemble VTach, VFib, or asystole.
Figure 38-5 This patient was wrestling with his child. The movement of the leads caused the clinician to believe that the patient was in ventricular tachycardia. The rhythm returned to normal the second the patient stopped moving.
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Figure 38-6 This is not atrial fibrillation; the rhythm is regular. Interference by an electrical appliance in the room was the cause of this artifact. Turning off the machine caused the baseline to return to normal.
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Figure 38-7 No, this patient was not having a VFib cardiac arrest! The lead was moving on his chest as he changed his robe.
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Figure 38-8 No, this patient was not in an asystolic cardiac arrest! The lead fell off his chest.
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Take a look at your patient and use some common sense. If you see what looks like VFib but the patient is walking to the bathroom, he is not in VFib. On the other hand, if you see something that looks like VFib and your patient is sleeping, shake him and wake him up. This is the first thing you are taught to do in advanced cardiac life support (ACLS), and there is a reason for this. If you can’t wake him, he is in cardiac arrest. This discussion may seem like an insult to your intelligence, but we have seen seasoned clinicians begin CPR, when suddenly, the patient begins to smack him back. Treat the patient, not the monitor!